This invention relates to an absorbent for acidic gases, such as carbon dioxide, HCl gas, HF gas, etc., used to clean air, narcotic gas, etc., and a process for the production thereof.
Soda lime is widely used as an absorbent for carbon dioxide contained in air and narcotic gas. In general, it is produced by immersing calcium oxide in a concentrated sodium hydroxide aqueous solution, subjecting the solution to heat treatment and pulverizing the resultant aggregate into particles, by mixing calcium hydroxide with other hydroxide and water, heating the mixture and pulverizing the resultant aggregate into particles, or by some other method.
However, the soda lime produced as above has an irregular physical form and often has an acute angle partially. For this reason, the soda lime has a problem in that when it is packed in a container, etc., and shipped, its individual particles grind one another by friction to crush the acute angles thereof, which results in formation of a fine powder or dust-like soda lime. That is, this fine powder or dust-like soda lime is inherently corrosive. For example, when there is used a device equipped with a column charged with this soda lime as an absorbent to remove carbon dioxide from a narcotic gas, the fine powder or dust of the soda lime is fed together with the narcotic gas and a narcotized patient might be seriously affected by breathing it in. Further, this soda lime may cause a problem in that its dust flies away into a room and pollutes air in the room when the column is recharged.
There have been proposed a variety of methods to solve these problems. For example, these problems might be solved by coating particle of the soda lime with, e.g. a gelatin-like substance such as dextran, by adding carboxymethyl cellulose to the soda lime (Japanese Patent Publication No. 42-20464), by forming the soda lime into semisperical particles, or by some other method.
Soda lime particles produced according to these methods are not necessarily satisfactory as an absorbent in view of performance and cost. For example, the coating method not only increases the production cost, but also causes a problem in that the capabilitiy of absorbing carbon dioxide is reduced depending upon a gelatin-like substance used to coat the particles. The method using carboxymethyl cellulose is costwise unsatisfactory. Further, although the method of forming semispherical soda lime makes it possible, to some extent, to reduce physical shape-induced formation of a fine powder or duct in transportion, such a semispherical soda lime has a problem in that the formation of a fine powder or dust cannot be satisfactorily prevented due to its low hardness.